Capillary transport devices have been constructed with two surfaces spaced to cause flow of introduced liquid by capillary action, thus creating between such surfaces a zone of intended liquid transport. When the two surfaces are two opposed sheets sealed around their edges, liquid is introduced through an access aperture formed in one of the sheets, and trapped air vented, e.g., by a separate aperture. Such capillary transport devices have been used for analyzing liquids; one such device being shown in U.S. Pat. No. 3,690,836 wherein one of the opposing surfaces is an absorbent reagent-containing layer. The transported liquid reacts with the imbibed reagents to produce a visible color indicative of the analyte.
The above-described devices are generally limited to capillary flow between the opposing surfaces. Such flow distributes the liquid to, e.g., two absorbent test areas that define in part the opposing surfaces, as shown for example, in U.S. Pat. No. 3,715,192, issued Feb. 6. 1973. However, the number of different test areas that are possible is limited by the number that can fit within the total surface areas of the zone that are to be wetted by the liquid.
In my aforesaid related application Ser. No. 954,689, the liquid transport device described therein is capable of diverting flow to individual test areas or zones. Such zones, through separate, are provided by a pair of opposing surfaces that are extensions of the pair of surfaces providing the first transport zone. That is, each separate test zone branch extends from an opening formed by both opposing walls or surfaces providing the first zone.
Although such branching features are highly useful, there is a limit to the number of branches that can extend from openings formed by both the opposing walls. If additional zones could be extended from only one of the surfaces of the first zone, then additional tests could be conducted in such additional zones.
Prior to this invention liquid transport devices did provide additional capillary zones created by relatively small diverting apertures having a cross-sectional flow-through area of 0.2 mm.sup.2 or less. "Cross-sectional flow-through area" is used herein to mean the area measured transverse to liquid flow through that area. This area limitation was necessary, because with preferred hydrostatic heads and prior art aperture configurations liquid would not divert into larger apertures. Examples of such small diverting apertures, generally circular in shape, can be found in conventional devices.
The problem, however, is that the prior art transport zones fed by such small area apertures created sharply-curved menisci that would not wet a solid test element disposed at the end of the zone. Thus, one problem has been to devise a diverting aperture that will provide capillary flow in a zone of sufficient cross-sectional area to properly wet a solid test element at the end of the zone.
Still another drawback of apertures of 0.2 mm.sup.2 cross-sectional flow-through area or less is that test elements that are area dependent, such as ion-selective elements, tend not to develop a useful signal for such small cross-sectional flow-through areas.